Make project group and project cards more visually pleasing

[e-lo]

Right now they are gray blobs. What should we do? Hmm.

[billyc]

Even just a splash of color on each would wake things up a bit. I'm sick of flat icons... maybe some fancy background fullbleed images? hmm. We need an official Zephyr colorscheme.

[e-lo]

Agreed. I'll add "create color scheme" as a TODO. I sorta created a turquoise/gray scheme on main website zephyrtransport.org but am happy to modify.

Please add examples of websites you like w.r.t. "fancy background fullbleed image" and "not flat icons" :-)